Influence of wave on sediment resuspension and nutrients release from sediments, collected from Lake Taihu and Lake Chaohu, was studied in flume experiments. Under strong-wave conditions, concentrations of suspended solids (SS), total phosphorus (TP) and dissolved total phosphorus (DTP) in overlying water were increased significantly following the sediments re-suspension. During the experiments on sediments of Lake Taihu and Lake Chaohu, TP concentrations increased 6 times and 3 times, and DTP concentration increased 100% and 70% more than it in presuspension, respectively. Concentration of soluble reactive phosphorus (SRP) of experiment on sediment of Lake Taihu increased 25%. During the massive sediment suspension, the dissolved phosphorus in pore water and much of the phosphorus adsorbed by the sediment particles were released into overlying water. The phenomena in this wave flume experiment are quite similar to the situation observed in situ of Lake Taihu. The critical wave stresses of sediment re-suspension are nearly equal. The change of concentrations of SS, TP, and SRP was the same as that in situ situation.This study showed that concentrations of TP and SRP in lake water could be increased significantly by wave disturbance. Phosphorus release was significantly enhanced by wave disturbance at the beginning of massive sediment re-suspension, but decreased later.
SUN Xiaojing,ZHU Guangwei, LUO Liancong & QIN Boqiang Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, Nanjing 210008, China
Concentration variations of suspended solids (SS), total phosphorus (TP), dissolved total phosphorus (DTP), dissolved reactive phosphorus (SRP), and algae available phosphorus (AAP) in overlying water were ob- served during the coldest week in a year in Lake Taihu, a large shallow lake in China. Water samples at different water depths were collected with wind speeds of 8, 12, 0 and 0 m/s on 23, 24, 26 and 30 January 2004, respectively. On 23 Janu- ary 2004, SS concentration increased to 258 mg/L with a wind speed of 8 m/s lasting for 1 h. SS concentration kept increasing and reached to 507 mg/L when the strong wind lasted for 24 h and the peak value of wind-speed reached to 12 m/s on 24 January 2004. On 26 January 2004, SS concen- tration decreased to 51 mg/L with the wind speed smaller than 2 m/s lasting for about half a day. Then after five con- tinuous waveless days, SS concentration decreased to 21 mg/L on 30 January 2004. The observed results confirmed that sediments in Lake Taihu would be intensively suspended if the surface wind speed is greater than 8 m/s, and the mag- nitude of SS would increase with increasing wind-speed. Coupled with the intensive sediment suspending, concentra- tions of TP, DTP and SRP on 23 January were 0.210, 0.048 and 0.035 mg/L, respectively. And they were 0.299, 0.054 and 0.026 mg/L on 24 January, which were significantly higher than those on 26 and 30 January. SRP concentration on 23 January was twice as high as that observed on 30 January. It indicates that the strong wind may result in an outbreak re- lease of phosphorus. Moreover, AAP contents in suspended solids were 132, 97 and 226 mg/kg on 23, 24 and 26 January, respectively. Therefore, it could be estimated that this strong wind process resulted in 987 t of TP, 80 t of SRP and 167 t of AAP releasing from sediments into overlying water. Since such strong wind process is frequent in the area of Lake Taihu, dynamical release driven by wind-induced wave dis- turbance may be the main mode for internal release of phosphorus. It
